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August 3rd, 2011, 11:23 PM   #1
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Probability

1.Given that P(B)=1/2,P(B l A)=3/7, P(B l A' ) =2/3
Find P(A ? B) ,P( A U B ),P( A l B )

2.If P( A l B )=3/10,P( B' l A ) =2/3,A and B are independent,find P(B),P(A U B),P(A' l B ).

Please help me to solve the question step by step.I need help.
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August 4th, 2011, 03:22 AM   #2
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Re: Probability

Quote:
Originally Posted by hoyy1kolko
1.Given that P(B)=1/2,P(B l A)=3/7, P(B l A' ) =2/3
Find P(A ? B) ,P( A U B ),P( A l B )
If you mean by P(B l A) the conditional probabilty , I can give you an answer.
We know that
P(A&#39=P(B | A)P(A)+P(B|A&#39(1-P(A))" />
So
}{P(B | A)-P(B | A&#39}=\frac{1/2-2/3}{3/7-2/3}=7/10" />
then

also

and finally

What do you think ?
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August 4th, 2011, 09:34 PM   #3
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Re: Probability

I still don understand about the part

how do you come out the equation
p(B)=P(B l A)P(A) + P(B l A' )P(A')

and one part state that

P(A ? B)=P(A)P(BlA) ,i don understand why.i need explanation.
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August 5th, 2011, 05:35 AM   #4
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Re: Probability

Hello, hoyy1kolko!

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August 6th, 2011, 05:09 AM   #5
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Re: Probability

Thank for the excellent explanation.I get it now!!

i still need some help.

Two transistors are chosen at random from a batch of transistor containing ninety good and ten defective ones.

a)If at least one out of the two transistors chosen is defective,find the probability that both transistors are defective.

This are the part that i can't solve in this question.I need help.and explanation.
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